A basic understanding of the means by which images are acquired and processed in the cardiac catheterization laboratory should be a fundamental part of every cardiology training program. This review outlines the entire X-ray system step-by-step by following the flow of energy from the generator to the monitor display. In addition, an overview of the major issues in radiation safety are discussed in simple terms focusing on both occupational and patient exposure, and the ways to minimize radiation dosage. Cathet Cardiovasc Intervent 2001;54:126-135.